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• BONYTAIL CHUB Little is known about the biological requirements of the bonytail chub, as the species greatly declined in numbers in the upper basin shortly after 1960. Until recently, FWS considered the species extirpated from the upper basin; however, a recently collected specimen which exhibits many bonytail characteristics could indicate a small, extant population. It is thought that, should this species persist in the Colorado River, the preferred habitat would be larger river reaches in the Colorado River. Conservation measures outlined below will contribute to conservation efforts for the bonytail chub, thus offsetting the likelihood of jeopardy for the species. CONSERVATION MEASURES The II.S. Fish and Wildlife Service (FWS) believes that any Further water depletions from the IIpper Colorado. River Basin (UCRB) may have detrimental effects on listed fishes. However, it is believed that certain management techniques can be implemented to offset harmful effects from additional development, particularly in the case of small depletions such as this. Impacts resulting from seemingly small water developments may be subtle, but harmful in a cumulative sense. The fact that water is depleted from the rivers reduces the flexibility of the system to withstand additional water ~ losses without detrimental impacts to essential areas. Creation of habitat favorable to introduced species is an example of how seemingly minor changes in flow regimes may shift the balance between survival and extinction for one or all of these listed fishes. Depletions that bring present day flows down to lower levels can occur if enhancement measures contained in active research and management plans are funded by the project sponsor or proponent. FWS has identified certain conservation measures that are currently considered necessary to maintain the survival of the fish and contribute toward their conservation. These measures include monitoring known populations and attempting to locate new areas containing the fish; further analyzing the potential effects of water depletions and associated flow regime modifications; locating existing and potential spawning and rearing areas; researching and constructing various fish passage and habitat restoration features; and producing the fish in a hatchery facility for research and restocking of individuals in existing and historical habitat. Since such measures will develop critically important data on the survival needs of the fish, attempt to restore essential habitat, and allow a conservation program to be implemented, funding of these activities by project sponsors is considered a reasonable and prudent alternative designed to compensate or prevent the adverse effects of water depletion. Under a procedure developed by the FWS, Upper Basin project sponsors are assessed a proportion of the total cost needed to support these conservation measures, currently estimated at approximately 25 million dollars. 3